The subject invention relates to ink jet printing, and more particularly to an ink jet dot detection system having a movable strip of print media on which test dots are printed.
An ink jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes called xe2x80x9cdot locations,xe2x80x9d xe2x80x9cdot positions,xe2x80x9d or xe2x80x9cpixelsxe2x80x9d . Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
An ink jet printhead includes an array of nozzles through which droplets of ink are fired, and the quality of the printed images produced by an ink jet printer depends to a large extent on whether nozzles are operative and the directionality of the ink drops emitted by the nozzles. Inoperative nozzles are sometimes called missing nozzles while drops that are not properly directed are sometimes called mis-directed drops. A nozzle that emits mis-directed drops can also be called a mis-directed nozzle.
Some ink jet printing devices include mechanisms for detecting missing and/or misdirected nozzles, so that such nozzles can be compensated to varying degrees by using an appropriate print mode or so that the user can be notified that too many nozzles are missing and/or misdirected. Print mode refers to the manner by which dots are placed on the print media. Techniques for detecting missing and/or misdirected nozzles include for example optical drop detectors comprised of a light source and a light sensor, and a patterned aperture. The operability and/or directionality of individual nozzles is/are detected by controlled energizing of the nozzles and detection of the presence or absence of ink drops in the light path between the light source and the light sensor. A consideration with optical drop detection is contamination of electro-optical elements by ink aerosol.
Another technique for detecting missing ad/or misdirected nozzles involves printing on a sheet of print media test patterns that are optically detected. Considerations with printing test patterns include the inconvenience to the user who will need to insert appropriate media (to avoid using expensive media such as photo media for testing) and later discard the print tested media.
There is accordingly a need for an efficient technique for detecting missing and/or mis-directed ink jet nozzles in an inkjet printing device.
The disclosed invention provides for an ink jet printing system that includes a print media strip dispenser that advances a strip of test print media through a test print zone and then through a detect zone. Test dots are printed on a test portion of the print media strip that is in the test print zone, and such test portion is then advanced to the detect zone for detection by an optical detector. Pursuant to such print media strip advance, another test portion of the print media strip is advanced into the test print zone and ready for printing of further test dots. By way of specific implementation, the print media strip dispenser comprises a cassette that includes a supply reel on which a strip of unprinted print media has been wound and a take-up reel for receiving the strip of test printed media after printing and detection of test dots.